Differential goods generically referred to as new synthetic fiber materials, which retain good characteristics of general synthetic fibers, are composed of raw yarns of different types having their own peculiar characteristics, such as microfibers, modified cross-section yarns and yarns composed of differently shrinkable fibers, and are prepared through composite conjugation or mere combination of such raw yarns, Because of their particular quality and feel of, for example, silk-like materials, peach skin materials and rayon-like materials which natural fibers do not have, the marketability for said new synthetic fiber materials is greatly expanding.
However, the dyeing of these composite materials as comprising microfibers, often involves various problems such as those mentioned below.
(1) The amount of light reflecting on the surfaces of the fibers increases, thereby lowering the visual depth of shade of the dyed materials.
(2) The dyed materials become poor light fastness, as being easily oxidized or reduced in light.
(3) Because of (1), the amount of dye used per unit area of the material shall increase, thereby lowering the sublimation and wet fastness of the dyed materials.
(4) The materials are dyed unevenly, as comprising composite fibers having different thicknesses.
In order to solve these problems, not only dyes having excellent buildup property and high fastness must be used but also dyes capable of level dyeing or good solid shade dyeing materials, which are composed of yarns having different thicknesses must be used.
If such composite materials are desired to be dyed in navy blue or black, it is said that the amount of the dye to be used must be from 2 to 5 times that of the dye for ordinary color. However, at present, no dye that is satisfactory for that purpose is commercially available to develop dyes that may be satisfactorily used for that purpose.